1. Field of the Invention
The present invention relates to polypropylene-based films and sheets having good ultraviolet shieldability, especially to such films and sheets that the ultraviolet absorbent additive existing therein does not bleed out, while they are stored, to detract from the outward appearance of the films and sheets stored.
2. Description of the Related Art
Heretofore, vinyl chloride-based resins have been used for surface-protective films for construction materials, furniture, etc. Because of the environmental problems with them, however, safer materials alternative to them are being investigated.
Polypropylene-based resins could be taken into consideration as candidates for the alternative materials, but their weather resistance is poor. Therefore, in order to establish the formulation of additives to the resins, especially to those for printed films, sheets and dry lamination films as laminated with adhesive, various studies have been made relating to the weather resistance and the adhesiveness retentivity of the films and sheets of the resins (see JP-A-5-92514, JP-A-6-212033).
In the additive formulation, it has heretofore been said that additives that vaporize less on molding are better, for which the data of heating loss are regarded as important. Surprisingly, however, it has been noted that, while shaped products of films or sheets are stored for about 10 days or so after their production, the additives existing therein often bleed out to greatly detract from the outward appearance of the films and sheets stored. The problem is often serious, but the reason for it is not clear.